1. Field of the Invention
The present invention relates to a process for the preparation of alkaline metal salts of polyethoxycarboxylic acids, useful as surfactant agents.
2. Background of the Related Art
A process is known in the art for the preparation of alkaline metal salts of polyethoxycarboxylic acids by means of the condensation of polyethoxylic alcohols with chloroacetic acid, or alkaline chloroacetate, in particular sodium chloroacetate, in the presence of an alkaline hydroxide, according to the reaction: ##STR1## This reaction does not arrive to its completion, or to its substantial completion, when the reactants are used in stoichiometric quantities and high conversions of the reactants are obtained only with long reaction times (of the order of 1-2 days), and using an excess of up to 50% of alkaline chloroacetate and of alkaline hydroxide, as it appears from the disclosure of German Pat. No. 2,418,444.
Together with the desired reaction product, considerable quantities are always present of alkaline glycolate and of alkaline chloride, as well as of unconverted alcohol.
Therefore, to be used, the alkaline salt of polyethoxycarboxylic acid requires a preliminary purification, and said purification is usually carried out by liberating the polyethoxycarboxylic acid from its salt by means of the treatment with a mineral acid, such as sulphuric acid and hydrochloric acid. The so separated polyethoxycarboxylic acid is then salified with alkaline hydroxide. In this treatment, the reaction byproducts, such as the alkaline glycolate and the alkaline chloride, are, separated by being dissolved in the aqueous phase during the treatment with mineral acid.
The unconverted polyethoxylic alcohol remains, on the contrary, inside the organic phase, together with the polyethoxycarboxylic acid. The process described, therefore, is affected by drawbacks, from the view points of complexity, conversion of the reactants into the useful reaction products and of the economic burdens.
In the art the possibility is moreover known generally of oxidating organic compounds of the type of alcohols into their correspondent carboxylic compounds, by means of the catalytic oxidation of said alcoholic compounds on catalysts of noble metals.
Such a technique has, however, had a poor commercial success, due to the difficulties deriving from the regeneration, recovery and reuse of the catalyst used for the purpose, as well as because the reaction originates often compounds at different oxidation level, with a consequent low yield in the desired useful product and the need for separation and purification treatments. Difficulties exist indeed for stopping the oxidation process at the desired level and avoiding the formation of undesired oxidated products, such as, e.g., peroxides.